1. FIeld of the Invention
The invention relates to machines for winding wire or similar elongated materials on a spool having a circular cylindrical core and end flanges; and more particularly, to such a machine with which it is desired to wind very neatly layered coils having successive layers running in opposite helical directions.
Spooling machines, of greater or lesser complexity, have been in use for many years for winding cordage, wire, thread, and tape-like materials. Neatness of winding has long been recognized as desirable because this reduces snagging of the material when it is subsequently unwound from the spool, and also because it maximizes the total length of material which can be wound on a given spool. The seriousness of the problems encountered in spooling operations is a function both of the characteristic of the material to be wound, and the configuration of the spool. Maximum storage density calls for the use of a spool having a minimum core diameter consistent with the characteristics of the cross-section of the material to be wound. An added complication, which relates to the characteristics of the material being wound, is that some materials exhibit a relatively high friction which tends to cause one turn to climb onto the next preceding turn, rather than lying alongside. The regularity of the surface or cross-section of the material also affects the ease with which one turn can be caused to lie neatly alongside the next preceding turn, or to follow a regular helical pattern onto a layer underneath. All of these problems become especially important if the material to be wound has a surface coating which is fragile or is easily damaged.
Special constraints on the spooling techniques are imposed whenever the material being spooled is coming from a process machine, and the nature of the upstream process requires that the material leaving that process be handled in a particularly gentle way. For example, metal wire is normally considered to be relatively strong. However, for certain applications relatively thin, flat wire configurations are desired using high cost materials such as tungsten or molybdenum which may, in addition, have gold plating applied to the exterior. Such a wire or ribbon coming from the plating machine must be taken up on a spool with extremely low tension, while at the same time especially regular spooling is desired without harsh rubbing of one turn over the edge of the next preceding turn. 2. Description of the Prior Art
Automatic spooling machines have been in use for many decades, with the nature of the machine control and mechanization being related to the economic importance of optimizing the resulting layers or turns. Thread, string and other cordage can be sold in very large quantities more easily and economically if they are wound in neatly spooled packages. Therefore relatively sophisticated machines using various mechanically controlled guiding systems have been used. However, these materials were neither especially fragile nor hard to handle.
Where relatively small quantities of hard-to-handle materials are to be spooled, the use of sophisticated purely mechanical control systems is disadvantageous because of the large set-up time involved; and also sometimes because of the relatively high maintenance costs involved for these machines.
The advantage of an electrical feedback control system for spooling is described in U.S. Pat. No. 3,779,480. The machine disclosed in this patent utilizes a sensing arm for detecting the angle at which heavy, stiff cable approaches the "run-on" point where the cable comes in contact with the spool core or the underlying layer. The desired transition between one layer and the next is described as being formed by having a traverse mechanism, by which a spool onto which cable is wound is translated back and forth in the direction of the spool axis, come to a stop while a first turn of a new layer is wound substantially parallel and to and in contact with the end flange. After the first turn of a new layer has been formed, substantially parallel to and in contact with the end flange, the portion of the cable approaching the run-on point is deflected sideways or axially by the characteristics of its smooth cylindrical surface, which militates against the formation of a next turn directly on top of the first turn. This axial displacement of the portion of wire is detected by a sensor, which causes the traverse mechanism to commence moving the spool in such a way that the cable approaching the spool is perpendicular to (that is, lies in a plane perpendicular to) the spool axis; while the cable being actually wound on the spool has a helix lead angle which is a function of the ratio of the diameter of the cable to the diameter of the layer being wound. Thus, this patent suggests that the lead angle of the material being wound should be 0.degree., so that there is not need to reverse a direction of lead angle for the two directions of traverse.
More recently, a far more sophisticated spooling machine is described in U.S. Pat. No. 4,022,391. In this spooler the spool rotational velocity is measured by a tachometer; the position of the spool traverse mechanism is measured by a position sensor such as a potentiometer or a digital position sensor; and the lead angle of the portion of wire between a fixed guide pulley and the run-on point is also measured. All of these values are fed to a processing circuit which controls in different ways the operation of the traverse motor in each of two phases of winding. During the normal phase, after enough turns of a new layer have been wound, the attitude angle by which wire approaches the run-on point is adjusted to a lagging angle, so as to force each new turn tightly against the preceding turn. The traverse mechanism will now operate at a substantially constant velocity until the run-on point has reached a predetermined distance from the end flange for this layer.
During a transition phase, as the wire wraps approach the flange, the angle of attitude is varied so as to reach zero just as the last turn touches the end flange. Preferably, this involves a continuous and uniform change in traverse speed. As in the U.S. Pat. No. 3,779,480 described above, the traverse continues at zero until one or more turns of the next layer have been wound, when the traverse resumes at its normal rate.
The machines described in the above patents suffer the disadvantage that it is difficult to obtain neat windings when the article to be wound does not readily slip into place alongside the next previous turn. Thus, especially if a delicate flat ribbon is to be wound at low tension, the machines of the prior art are apt to produce uneven transition turns at the end of a layer, with resulting damage to the wire if it is delicate.